Trees are fascinating creatures, and learning about their ways can keep you entertained for a lifetime. Their symbiotic relationships with their surroundings are fascinating, as is photosynthesis and their reproductive systems.
One other fascinating thing about trees is that you can reliably tell how old they are down to the year by observing their bodies. With humans and most other animals and plants, this is impossible. But because of the annual cycles that trees grow in, and the solid structure of their trunks and branches, we can read the records of their lives.
Yes, you can tell how old a tree is by reading the rings when the trunk is cut in a cross-section. Actually, you’re able to tell how old THAT PART of the tree is. In a large branch you can also count how long it’s been there in this way. Skilled arborists can even gain other information from looking at tree rings. And arborist can gather fairly accurate info about whether there were droughts, disease or damage in the tree’s history.
What Makes This Possible?
The wood of a tree grows fast in spring, and is lighter because it consists of larger (more moist) cells, so the pigment distribution is less dense. In summer, it’s dryer and growth is slower; the wood forms smaller cells and looks darker. Fall and winter there is no growth worth noting. So when the tree is cut, the layers appear as alternating rings of light and dark wood. Each light/dark set is one year of growth, so either count dark or light rings, but not both.
The main drawback of using this amazing natural record-keeping system is that you have to cut down your tree. It is possible to bore a sample without killing the tree, but not without hurting it. So for highest accuracy, you really have to wait until the tree is removed or at least cut down to get it’s age.
What if The Tree is Still Standing?
There is a way you can take measurements and use some math to estimate tree age. It’s outlined here by the state of Michigan Athens-Clarke County Community Tree Program: Estimating Tree Age. Doing this tree age estimation can be just as fun and counting rings, and you get to keep your tree! This uses some math that is high school or college level, so get help if you need it!
Another interesting way to figure out the age of a tree is to look up historical photos of the property the tree is on. Or if it’s near a building, find out when the property was built and if the trees were put in at the same time. This tracing the history of the are usually can give you a ballpark idea, but not exact year of planting.